METHOD OF MAKING MnGaGe FILMS

ABSTRACT

A method of making ferromagnetic films of MnGaGe upon a substrate, the films crystallizing in the tetragonal structure and having a grain size of less than one-half micron, made by the method of depositing a first layer of either manganese, or gallium and germanium upon a heated substrate, followed by the deposition of the remaining material upon the first layer, and annealing the deposited layers at a desired temperature until a homogeneous composition is achieved, and then cooling of the film-substrate combination. In this manner, with appropriately chosen temperatures, films having a grain size of less than onehalf micron and being particularly usable for storage applications may be fabricated.

[4 1, Nov. 26, 1974 [54] METHOD OF MAKING MnGaGe FILMS v [75] Inventors: Kenneth Lee; James Carr Suits,

both of Saratoga, Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Feb. 23, 1973 [21] Appl. No.: 335,405

[56] References Cited UNITED STATES PATENTS 3059,5311 10/1962 Sherwood et a1 117/235 3,065,071 11/1962 Wernick 75/134 3,126,346 3/1964 Bither 75/134 3,147,112 9/1964 Bither 75/134 3,207,638 9/1965 Bither 75/134 3,279,914 10/1966 Bither 75/134 3,619,289 l/1968 Di Chen 117/235 3,676,867 7/1972 Bacon et a1 75/134 Primary Examiner-William D. Martin Assistant Examiner-Bernard D. Pianalto Attorney, Agent,,0r Firm-1oseph G. Walsh [57] ABSTRACT A method of making ferromagnetic films of MnGaGe upon a substrate, the films crystalllizing in the tetragonal structure and having a grain size of less than onehalf micron, made by the method of depositing a first layer of either manganese, or gallium and germanium upon a heated substrate, followed by the deposition of the remaining material upon the first layer, and annealing the deposited layers at a desired temperature until a homogeneous composition is achieved, and then cooling of the film-substrate combination. In this manner, with appropriately chosen temperatures, films having a grain size of less than one-half micron and being particularly usable for storage applications may be fabricated.

8 Claims, No Drawings METHOD OF MAKING MnGaGe-FILMS FIELD OF THE INVENTION This invention relates to methods of making ferromagnetic films in general and ferromagnetic films in particular characterized by having a fine grain structure.

PRIOR ART The new ferromagnetic material MnGaGe crystallizing in the tetragonal structure has been disclosed in the copending patent application of Street and Sawatzky entitled Ferromagnetic Material, filed Sept. 15, 1972, as application Ser. No. 289,512, which is a continuation-in-part of application Ser. No. 202,642, filed Nov. 26, 1971, now abandoned and assigned to the Assignee of this invention. Various compositions of the MnGaGe material are disclosed as well as the physical properties and particularly the magnetic properties of the material. This material finds particular application in magneto-optic data storage applications due to its low Curie point and high Faraday rotation. The application of Street and Sawatzky above, is incorporated into this application for its teachings of the particular material.

It is desirable for magneto-optic applications where readout of stored data is by the Kerr or Faraday effects, that the material has a high signal-to-noise ratio. This is most often achieved with a material. having a very fine grainsize. 1n the case of MnGaGe, a grain size of less than one-half micronis desirable to achieve signalto-noise ratios for particular storage applications. Thus, it is an object of this invention to describe a method for providing a fine grain ferromagnetic film of MnGaGe crystallizing in the tetragonal structure.

Another object of this invention is to provide a range of working temperatureswhereby this film may be deposited upon a substrate.

Another object of this invention is to provide alternative methods of depositing the film by vapor deposition and by sputtering techniques.

SUMMARY OF THE INVENTION These and otherobjects are met by the method of this invention. Briefly stated, the methodcomprises depositing a first layer of either manganese, or gallium and germanium, in the desired compositional amount as desired in the finished film, upon a substrate. maintained at a temperature of between 150 and 250C in an evacuated environment, and then depositing a second layer chosen from the other of the manganese or gallium and germanium upon the first layer. The combination is then annealed at a temperature between 200C to 475C until a homogeneous composition is obtained, and the film-substrate combination is then cooled. This results in a fine grain manganese-galliumgermanium structure. Additionalsuccessive layers may also be deposited, and temperatures may be chosen as to achieve a simultaneous annealing-deposition situatron.

The invention will thus be understood in relation to the following general description and claims.

GENERAL DESCRIPTION Y Manganese gallium germanium as described in the aforementioned Street and Sawatzky application, crystallizes in the tetragonal structure and has a potential range of Curie points as a function of the exact composition utilized. This film has proved valuable for magneto-optic storage applications. In attempting 'to achieve fine grain films which are most desirable in this type of application for high-density storage, we have found that films having a grain size of less than one-half micron may be obtained usingthe particular method described below. No other method has been found that consistently will produce grains of less than one-half micron in size. Before describing the method of our invention, it should be stated that the common technique of evaporating manganese, gallium and germanium, either simultaneously or each individually, and then annealing the film to achieve homogeneity, results in a grain size in excess of one-half micron, and is most typically approximately one micron or larger. These films also crystallize in the tetragonal structure and have their magnetization substantially perpendicular to the film plain. The tetragonal structure may be verified by the use of X-ray analysis, for example.

We have found that if a particular deposition method is carried out, we consistently prepare manganese-gallium-germanium films having a grain size of less than one-half micron. In this method, films are deposited upon a substrate either by sputtering or by vapor deposition. Where vapor deposition is utilized, it is preferred to have an atmosphere between 101 to 10" torr during deposition, although higher vacuums are acceptable. The substrate described may be rigid or flexible, magnetic or non-magnetic. Typically, a glass substrate, sapphire substrate, or molybdenum substrate may be utilized. It is important, of course, that the substrate not react with the filmbeing deposited. In both the sputtering or vapor deposition systems, the substrate is maintained at a temperature of between C to 350C, a desired and as discussed below.

First, a layer of manganese, for example, may be deposited upon the substrate at a rateof at least 1 A per second, with a preferred rate of 2 A per second. An amount ofmanganese is deposited so that the film composition after annealing will contain the desired amount of manganese. Then, a combined film of galliuni and germanium is deposited by the simultaneous combination with the already deposited manganese.

These amounts are easily calculated by those skilled in the art as a function of the desired final composition in conjunction with the known vapor pressures of the material. The composition may be measured by microprobe analysis.

After deposition of the film, the films are annealed while still in vacuum at between 200 and 475C until a homogeneous'composition is achieved, at which time the films are cooled. Measurement of the film grain size by optical or electron microscopic method shows films made in this manner have a grain size of less than onehalf micron.

When the temperature of the substrate is between 200 and 250, depending upon the particular composilayer. Where an initial substrate temperature of less than substantially 200C is utilized, a subsequent anhaving a grain size of less than one-half micron. Over 100 films have been made by the method of this invention, showing the small grain size to be reproducible over a variety of compositions by the technique of this nealing step is desirable. The following table shows var- 5 invention. The preferred embodiments are shown in ious compositions made by vapor deposition and by the above table. sputtering techniques, for various compositions of While this invention has been shown in its preferred manganese, gallium and germanium showing also subembodiments, variations therefrom will still remain strate temperature, the annealing temperature, the anwithin the scope and spirit of this invention and will be nealing time,the remanence, and the polar Faraday roi0 evident to those skilled in the art. Thus, a variety of tation, in degrees. substrates may be utilized, as well as the variety of de- (Atomic .l Sub Annual Anneul Rent. PFR Vapor Mn (iii (ie Temp C l cm [10C Time, hr. '77 deg.

.49 .23 .224 2m 100 .20 .50 .25 .25 150 210 1 70 .1x .46 .29 .25 210 45o l a 51 .72

.47 .22 .3t :00 i (in .57 .46 .2x .26 210 475 1 u.- so .34 .47 .25 2x 200 i i. 70 .42 .46 .3) .25 l5ll 4. 0 l f2 60 .70 Spult.

Each ofthe films in the table has its wavelength sensiposition rates, and temperatures, within the teachings tivity and other magnetic properties such as the Curie of thi i v ntion, temperature as described in the aforementioned Street Wh t i laimed i and Sawatzky application, as a function of the particu- 1, A method of making a fine grain ferromagnetic lar composition. The structures are all tetragonal as fil f M G G r l li i i h retragonal Struc. noted by X-ray analysis, and the magnetization is suffiture upon a substrate comprising the steps of: ciently perpendicular to the film plane to yield the redepositing a layer of Mn and a layer of (Ga Ge) in manences listed above. As compared to the simultah d i d compositional amount b d on h "eous evaporation teehnlque of evaporating all three at final desired composition in any desired order upon once, mentioned previously, the signal-to-noise ratio a Substrate i i d at a temperature b n y be imPKWed to a factor of ten to one in p substantially 150C to 250C as a first layer and a son with a previous three to one signal-to-noise ratio. Second M upon id fi t l Further, the films made y the layered teehnlque annealing the superimposed deposited layers at a scribed above yp l have 100 EMU/Ce magnetlza' temperature between substantially 200C and tion as a function of composition. Further, preferred 475C until a homogeneous Composition is films are in the 500 to 700 A thickness range. 40 achieved; and

While the invention has been particularly described cooling the film-substrate combination, whereby a where manganese is deposited first, followed by simulferromagnetic film of MnGaGe crystallizing in the taneous deposition of gallium plus germanium, the laytetragonal structure and having a grain size of less ers may be deposited in the opposite manner. Thus, galthan 0,5 mi i fo m d n th b t m lium and germanium may be simultaneously deposited, 2. The method of claim 1 wherein the substrate temfollowed by deposition of manganese, followed by the perature and MnGaGe compositional amounts are so annealing step. Further, alternative layers of the matechosen that the annealing step occurs simultaneously rial may be deposited with the same result being with the deposition of the second layer. achieved. Thus, alternating layers of manganese. gal- 3. The method of claim 2 wherein the substrate temlium plus germanium, manganese. gallium plus germaperature is chosen to be at least substantially 300C. nium, etc., may be employed. As before, irrespective of 4. The method ofclaim 1 including depositing addiwhich is the first layer, a substrate temperature may be tional sets of layers of Mn and (Ga and Ge) as desired chosen in relation to a particular composition so that while maintaining the desired compositional amount, the annealing step occurs simultaneously with the deprior to the annealing step. position of the second layer. The particular composi- 5. The method of claim 1 wherein the layers are detion for which this is achievable and the particular temposited y the method of Vapor deposltionperatures are easily arrived at by analysis of the depos- The method Offllalm 1 e ein the Mn, Ga and Ge ited film by techniques will known in the art, such as are each deposlted from a Separate e X43}, analysis 7. The method of claim 1 wherein the substrate is non-magnetic.

In the above table is also shown a sputtering technique which illustrates again that the multilayer deposition may be utilized in sputtered films to produce a film of each layer is at least lA/second. 

1. A METHOD OF MAKING A FINE GRAIN FERROMAGNETIC FILM OF MNGAGE CRYSTALLIZING IN THE TETRAGONAL STRUCTURE UPON A SUBSTRATE COMPRISING THE STEP OF: DEPOSITION A LAYER OF MN AND A LAYER OF (GA + GE) IN THE DESIRED COMPOSITIONAL AMOUNT BASED ON THE FINAL DESIRED COMPOSITION IN AN DESIRED ORDER UPON A SUBSTRATE MAINTAINED AT A TEMPERATURE BETWEEN SUBSTANTIALLY 150*C TO 250*C AS A FIRST LAYER AND A SECOND LAYER UPON SAID FIRST LAYER; ANNEALING THE SUPERIMPOSED DEPOSITED LAYERS AT A TENPERATURE BETWEEN SUBSTANTIALLY 200*C AND 475*C UNTIL A HOMOGENEOUS COMPOSITION IS ACHIEVED; AND COOLING THE FILM-SUBSTRATE COMBINATION, WHEREBY A FERROMAGNETIC FILM OF MAGAGE CRYSTALLIZING IN THE TETRAGONAL STRUCTURE AND HAVING A GRAIN SIZE OF LESS THAN 0.5 MICRON IS FORMED UPON THE SUBSTRATE.
 2. The method of claim 1 wherein the substrate temperature and MnGaGe compositional amounts are so chosen that the annealing step occurs simultaneously with the deposition of the second layer.
 3. The method of claim 2 wherein the substrate temperature is chosen to be at least substantially 300*C.
 4. The method of claim 1 including depositing additional sets of layers of Mn and (Ga and Ge) as desired while maintaining the desired compositional amount, prior to the annealing step.
 5. The method of claim 1 wherein the layers are deposited by the method of vapor deposition.
 6. The method of claim 1 wherein the Mn, Ga and Ge are each deposited from a separate source.
 7. The method of claim 1 wherein the substrate is non-magnetic.
 8. The method of claim 1 wherein the deposition rate of each layer is at least 1A/second. 